1. Field of the Invention
This invention relates to a device for holding a film on a focal plane, and more particularly to a device for holding a photographic film on a focal plane of an optical system like a microfilm in a microfilm camera or a microfilm reader.
2. Description of the Prior Art
In a microfilm camera or reader, the microfilm must be held accurately on the focal plane of the optical system thereof. In order to hold the microfilm on the focal plane, it has been known in the art to use a film pressure plate or a device utilizing the curl or solidity of the film. However, the pressure plate is disadvantageous in that the film is liable to be scratched when it is fed therethrough, and the device utilizing the solidity of the film is unreliable in operation.
In view of the disadvantages of the above mentioned devices, it has been proposed to utilize suction for holding the microfilm on a film support plate located on the focal plane. The suction device holds the film by suction on the plate while the film is to be held on the focal plane during exposure or projection and sets the film free when it is to be fed. This method of holding the film on the focal plane comparatively accurately holds the film on the focal plane, but is slow in operation since the turn ON and OFF of the system are controlled by an electromagnet or the like.